Apart from strictly acoustic instruments, it has become common practice to equip stringed instruments such as guitars with electronic sound reinforcement, typically, in an “electric” guitar, utilizing a magnetic pickup device that senses vibration of steel strings electro-magnetically, or in an “acoustic” instrument with non-metallic strings, utilizing a microphone pickup. The audio signal from the pickup is normally transmitted from the guitar to an external power amplifier/sound reinforcement system via a flexible audio cable fitted at each end with a connector plug, typically of the well known quarter-inch audio phone plug type, one end engaging a mating phone jack mounted in a suitable location on the instrument and the other end engaging a mating phone jack at the input of the external amplifier.
Many such instruments are in use without on-board amplification, with the pickup signal, usually modified by passive controls/components, fed directly at relatively high source impedance via the flexible audio cable. Such passive high impedance systems are inherently subject to environmental interference such as power line hum and to audio/musical performance degradation as a function of cable type, length, shielding integrity, characteristic impedance and termination impedance. As a technological refinement to mitigate such problems, with the advance of electronic technology there has been a trend to provide active on-board electronics: at least a pre-amplifier and buffer, typically powered from an on-board battery. The resultant lower source impedance and higher signal level make the system inherently far less vulnerable to degradation due to the above-mentioned audio cable variations, allowing much greater cable lengths and offering the player the potential of a wide variety of on-board control capabilities and special musical performance effects.
Guitars and other lute family instruments are typically supported for playing purposes by a shoulder strap attached to opposite ends of the guitar. At the body end, it is traditional to provide a central “strap-peg” or “end-pin” made of wood, plastic or metal, and configured with an annular flange to engage an opening, e.g. a slotted hole, in the shoulder strap end in a manner that is both secure for playing and readily removable.